Multi-coordinate measuring apparatus are available in the most different configurations. An overview of the different constructions is provided in an article by M. Dietsch and H. Lang in the publication entitled "Feinwerktechnik and Messtechnik 86", 1978, pages 262 to 269. All of the apparatus described therein are in principle based on the same configuration. The apparatus comprise three guides arranged so as to be mutually perpendicular and assembled one atop the other. The measuring probe is displaceable along these guides and the apparatus further include three linear scales corresponding to respective ones of the guides.
The first guide must carry the weights of each of the further guides which are built thereupon. For this reason, a stable configuration of the guides which prevents deformation during the measuring operation is required in order to obtain an adequately high measuring precision. Coordinate measuring apparatus are therefore expensive and complex measuring instruments.
Coordinate measuring apparatus are also known which do not measure in a cartesian coordinate system and instead measure in spherical or cylindrical coordinates. For example, British Patent No. 1,498,009 describes a coordinate measuring apparatus wherein the measuring head is movably held by means of three joints arranged one behind the other. The position of the measuring head in this apparatus is determined by angle encoders arranged in the joints.
A similarly configured coordinate measuring apparatus is disclosed in U.S. Pat. No. 4,240,205. In this apparatus, the measuring head is attached to a vertically displaceable probe shaft which, in turn, is guided in a plane by means of three joints having a vertically arranged rotational axis. The position of the sleeve in the plane is measured with the aid of a measuring scale and a rotational transducer. Also in both of the last-mentioned apparatus, the movable parts of the apparatus are braced on each other utilizing rotational axes for guiding the measuring head instead of linear guides. It is therefore necessary to utilize counterweights by means of which the movable machine parts must be counterbalanced and which increases the weight and mass of the movable machine parts. Furthermore, it is necessary to configure the bearings for the rotational shafts so that they are very stable since these shafts must each carry the weight of the part built up thereupon.
However, it is still not possible to carry out adequately precise measurements with these apparatus since the individual parts of the linkage arm are subjected to changing load relationships during the measurements and therefore deform in an uncontrolled manner.
So-called elevation measuring apparatus are also known. These apparatus comprise a carrier which is manually freely displaceable in a plane and on which a linear measuring probe is displaceably guided in the vertical direction. With the scale corresponding to the guide, only the elevation of the measuring probe above the plane at different locations can be measured and brought into relationship. The position of the elevation measuring apparatus in this plane is not detected. In addition, the measuring head of the elevation measuring apparatus is pivotable outwardly only along the vertical if at all.
These known measuring apparatus are therefore not multi-coordinate measuring apparatus since they are suitable for measuring in only a single dimension. An elevation measuring apparatus is known which is guided in two coordinates via a frame and whose position coordinates in the plane are determined by means of the scales corresponding to the arm guides. However, this apparatus corresponds again to the initially mentioned configuration of known multi-measuring coordinate apparatus and has disadvantages which include the condition that orthogonal errors of the guides are incorporated directly into the measuring result. Furthermore, this known apparatus can not rotate so that a rotatable table for the workpiece to be measured is additionally required.
German published patent application Nos. DE-OS 3,205,362 and DE-OS 3,629,689 disclose coordinate measuring apparatus which are based on a measuring element guided by hand or by a robot over the workpiece to be measured. The workpiece is measured from different directions with the aid of laser distance measuring devices. However, these apparatus incorporate the disadvantage that the angular alignment of the measuring element can only be determined with great effort and even then not in every position in the measuring space. Furthermore, one can not pass around the workpiece to be measured with the measuring element since at least several of the measuring rays would be interrupted.